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Algebra Difficulty 5.9 AIME, harder Prove it

Example 12 Real numbers x,y,zx, y, z satisfy xyz=8x y z=8. Prove:
22+x2+22+y2+22+z21\frac{2}{2+x^{2}}+\frac{2}{2+y^{2}}+\frac{2}{2+z^{2}} \geqslant 1

Solution

Proof: Let x2=u3,y2=v3,z2=w3x^{2}=u^{3}, y^{2}=v^{3}, z^{2}=w^{3}, then equation (36) can be rewritten as
vwvw+2u2+wuwu+2v2+uvuv+2w21,\frac{v w}{v w+2 u^{2}}+\frac{w u}{w u+2 v^{2}}+\frac{u v}{u v+2 w^{2}} \geqslant 1,

where u,v,wu, v, w are positive real numbers, and satisfy uvw=4u v w=4.
Since
vwvw+2u2+wuwu+2v2+uvuv+2w21=uvw(u+v+w)[(vw)2+(wu)2+(uv)2](2u2+vw)(2v2+wu)(2w2+uv)0\begin{aligned} & \frac{v w}{v w+2 u^{2}}+\frac{w u}{w u+2 v^{2}}+\frac{u v}{u v+2 w^{2}}-1 \\ = & \frac{u v w(u+v+w)\left[(v-w)^{2}+(w-u)^{2}+(u-v)^{2}\right]}{\left(2 u^{2}+v w\right)\left(2 v^{2}+w u\right)\left(2 w^{2}+u v\right)} \geqslant 0 \end{aligned}

Therefore, equation (37) holds, which means equation (36) holds.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.